This invention concerns a process and equipment for melt processing a thermoplastic polymer. Specifically, the invention concerns a process and equipment for melt processing a thermoplastic polymer wherein a portion of the surfaces which contact the thermoplastic polymer, while said thermoplastic polymer is in a heat plastified state, comprises boron carbide.
Methods and equipment for melt processing thermoplastic polymers are well-known in the prior art. Typically, such methods and equipment involve passing the heat plastified thermoplastic polymer through processing equipment, the surfaces of which comprise a metal or metal alloy.
In those cases wherein the thermoplastic polymer contains a halogen, passing the heat plastified halogen containing thermoplastic polymer over certain metal surfaces is known to lead to dehydrohalogenation within the polymer. For example, in the processing of vinylidene chloride interpolymers, contacting the heat plastified vinylidene chloride interpolymer against a surface containing iron has been found to lead to the rapid dehydrohalogenation and subsequent decomposition of the vinylidene chloride interpolymer.
Moreover, it is also known that certain thermoplastic polymers while in a heat plastified state adhere to certain metal or metal alloy surfaces. Adhesion between the heat plastified polymers and the metal or metal alloy surfaces of equipment used to process said polymers is undesirable. Adhesion between the heat plastified thermoplastic polymer and the metal or metal alloy surfaces of the processing equipment cause portions of the thermoplastic polymer to remain within the processing equipment for undesirable periods of time. The longer a thermoplastic polymer remains within the processing equipment while in a heat plastified state the more likely said thermoplastic polymer is to experience detrimental effects caused by heat. Additionally, adhesion between the heat plastified thermoplastic polymer and the processing equipment tends to make movement of the heat plastified thermoplastic polymer through said processing equipment more difficult.
Recognition of these problems has caused a great deal of research to be done in determining which metal or metal alloys are best suited for processing particular thermoplastic polymers. Often, it has been found that particular thermoplastic polymers process best on metal or metal alloy surfaces which metal or metal alloy surfaces are expensive to produce or difficult to fabricate. For example, vinylidene chloride interpolymers have been found to process best on highly polished metal surfaces which surfaces comprise an alloy of nickel.
It is desirable to find a material suitable for processing thermoplastic polymers which material is relatively inexpensive, easy to fabricate, and avoids the problems of adhesion and decomposition discussed above. It is to this goal that the present invention is directed.